Dielectric barrier layer for increasing electromigration lifetimes in copper interconnect structures

ABSTRACT

Embodiments of the invention include a copper interconnect structure having increased electromigration lifetime. Such structures can include a semiconductor substrate having a copper layer formed thereon. A dielectric barrier stack is formed on the copper layer. The dielectric barrier stack includes a first portion formed adjacent to the copper layer and a second portion formed on the first portion, the first portion having improved adhesion to copper relative to the second portion and both portions are formed having resistance to copper diffusion. The invention also includes several embodiments for constructing such structures. Adhesion of the dielectric barrier stack to copper can be increased by plasma treating or ion implanting selected portions of the dielectric barrier stack with adhesion enhancing materials to increase the concentration of such materials in the stack.

RELATED APPLICATION

This is a Divisional application of U.S. application Ser. No.10/414,601, entitled “DIELECTRIC BARRIER LAYER FOR INCREASINGELECTROMIGRATION LIFETIMES IN COPPER INTERCONNECT STRUCTURES”, filed onApr. 15, 2003 now U.S. Pat No. 7,276,441, which is incorporated hereinby reference and from which priority under 35 U.S.C. §120 is claimed.

TECHNICAL FIELD

The invention described herein relates generally to semiconductordevices and processing. In particular, the invention relates tosemiconductor structures and processes that can be incorporated intoimproved copper interconnection structures having longerelectromigration lifetimes. And most particularly, the invention relatesforming an improved dielectric barrier layers formed on copper metallines and layers.

BACKGROUND

The semiconductor industry has moved ever increasingly to copperconductive lines and interconnect structures in the construction ofsemiconductor devices. Copper has proven to be a very useful material.Especially, advantageous is the low resistivity relative to othercomparable process materials (e.g., aluminum). As a result, coppercircuitry suffers less from resistance-capacitance (RC) delays. Thismakes copper systems faster.

However, copper materials have the disadvantage of high diffusivitythrough dielectric and silicon materials on which the copper isdeposited. This is especially problematic when copper is used withso-called low-κ dielectric materials, which are coming into increasinglycommon usage. Diffusion of copper into insulating layers comprised oflow-κ dielectric materials can result in serious problems. Diffusion ofcopper into low-κ materials degrades the dielectric performance of suchmaterials and commonly leads to device failure. The industry has adaptedto this problem by implementing a wide range of barrier layers toprevent the diffusion of copper into the affected materials. Typically,the barrier layers consist of thin layers of barrier material interposedbetween copper layers and low-κ dielectric layers.

Although such barrier layers are effective at preventing the diffusionof copper materials, such barrier layers suffer from their own set ofdifficulties. One such problem is that barrier layers can contribute toelectromigration induced voiding in copper interconnect structures. Suchvoiding is a common source of circuit failure in copper basedsemiconductor structures. Such voiding is particularly problematic whenit occurs in via structures. Research has shown that electromagneticvoiding is particularly common at the interface between the copper layerand the barrier layer.

This problem can be illustrated with reference to the schematiccross-section views illustrated in FIG. 1( a) and FIG. 1( b). In FIG. 1(a), a conventional multi-level semiconductor substrate 100 is depicted.A wafer surface is depicted with a copper line 104 formed therein. Thecopper line 104 is typically formed using copper or copper-containingmaterials (e.g., copper alloys or copper laminates and the like).Insulating layers 105, 106 comprised of electrically insulating material(e.g., SiO₂, low-κ dielectrics, and other like materials) are formed onthe wafer surface to provide dielectric insulation between metal linesand between layers. Other copper layers 107 are used to electricallyinterconnect the various layers of an IC through via or other electricalconnection structures. In the depicted example, a copper layer 107 isformed in an opening formed in the insulating layer 105. The openingexposes underlying copper line 104. Such openings are commonly formedusing damascene or dual-damascene fabrication processes. However, whencopper is used in such processes, barrier layers are used to preventcopper from diffusing out of its intended location so that the copperdoes not “poison” the low-κ layers used in such semiconductorstructures.

These barrier layers take the form of refractory metal barrier layers110 and so-called dielectric barrier layers 111. Commonly, refractorymetal barrier layers (metal barrier layers) 110 include refractorymetals in their construction. Such refractory metal barrier materialscan include tantalum (Ta) or titanium (Ti) based barrier materials(e.g., tantalum nitrides (TaN), tantalum silicon nitrides (TaSiN), ortitanium nitrides (TiN)). Additionally, multi-layer refractory metalbarrier layers can be formed. Also, graded metal barrier layers can beused.

Additionally, so-called dielectric barrier layers are used. Suchdielectric barrier layers prevent copper diffusion but do notincorporate refractory metals in their construction. Typical examples ofsuch dielectric barrier layers are formed of dielectric materials thatinclude silicon carbide and silicon carbon nitride. Such materialsgenerally have a relatively lower dielectric constant (κ) than therefractory metal barrier layers. However, it would be desirable to makeuse of dielectric barrier layers that have lower effective κ values.

Others have discovered that copper layer and line commonly includeminute voids 108. Others have also discovered that during the ordinaryoperation of integrated circuit devices, copper atoms migrate within thecopper lines 104 and layers 107. One of the unfortunate byproducts ofsuch copper migration is that the voids 108 in the copper layers andlines also tend to migrate. Moreover, at certain points in such linesand layers the voids also tend to aggregate causing large “macrovoids”that can cause serious problems for circuit operation. If suchmacrovoids become large enough and form in the wrong locations they canand do cause circuit failure. One of the major pathways for such coppermigration and macrovoid formation is at the interfaces between thecopper layers (and lines) and the copper diffusion barrier layers (e.g.,the metal and dielectric barrier layers).

FIG. 1( b) shows one of the problems circuits undergo when coppermigration causes the voids 108 to move. In the depicted embodiment, thevoids 108 have migrated and aggregated to form macrovoids 108′ that arelarge enough to cause the depicted interconnect structure to fail. Asdepicted, the aggregate size of the macrovoids 108′ can become quitesizable reducing current through regions having voids. As depicted, theproblem becomes even worse when macrovoids 108′ migrate to narrowregions on in the semiconductor circuitry. As depicted in FIG. 1( b) amacrovoid 108′ has migrated to occlude the conduction pathway 103 (e.g.,a via). In short, the macrovoid 108′ has migrated to the interfacebetween the copper layer 107 (e.g., a via) and the metal line 104. Also,the macrovoid 108′ has grown so large that it destroys the current pathbetween the copper layer 107 and the metal line 104. Moreover, suchvoiding problems are known to become worse when low κ materials areused. Current solutions to this problem require that a secondary via beconstructed so that when one via fails a conduction path can still beachieved through the secondary via. Although such solutions work wellenough for their intended purpose, improved solutions are desirable.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, an improvedinterconnection structure and method for its fabrication are disclosed.

In general, the present invention is directed toward methods andstructures for constructing copper interconnect structures havingincreased electromigration lifetimes and a lower incidence of voidinduced circuit failures. Such structures include a dielectric barrierstack formed on the copper material. A first portion of the stack hasgood adhesion to the copper. The second portion has a low κ valuerelative to the first portion. Preferably, both portions operate asdiffusion barriers to copper. Such dielectric barrier stacks areconstructed to achieve good adhesion to copper and have a low overalleffective κ value while providing an effective diffusion barrier tocopper. The resultant structure improves the electromigration lifetimesof associated copper layers and lines.

One embodiment of the invention includes a method for forming a copperinterconnect structure. The method involves providing a substrate havinga copper layer formed thereon. A dielectric barrier stack is then formedon the copper layer. A portion of the dielectric barrier stack istreated with an adhesion enhancing materials to enhance the adhesion ofthe dielectric barrier stack to the copper layer.

In another related embodiment, the method of forming the dielectricstack comprises forming a first dielectric barrier layer and then plasmatreating the first layer with plasma that contains adhesion enhancingmaterials. A second dielectric barrier layer is then formed on theplasma-treated first dielectric barrier, thereby completing the stack.

In another related embodiment, the method of forming the dielectricstack comprises forming a first dielectric barrier layer and then ionimplanting the first layer of dielectric barrier material with adhesionenhancing materials. A second dielectric barrier layer is then formed onthe ion implanted first dielectric barrier, thereby completing thestack.

In another related embodiment, the method of forming the dielectricstack comprises forming a dielectric barrier layer and then ionimplanting the dielectric barrier layer with adhesion enhancingmaterials so that a portion of the dielectric barrier layer closest tothe underlying copper layer has an increased density of adhesionenhancing materials thereby increasing the adhesion of the dielectricbarrier layer to the underlying copper layer.

Another embodiment involves a novel copper interconnect structure havingincreased electromigration lifetime. Such a structure includes asemiconductor substrate having a copper layer formed thereon. Adielectric barrier stack is formed on the copper layer. The dielectricbarrier stack includes a first portion formed adjacent to the copperlayer and a second portion formed on the first portion, the firstportion having improved adhesion to copper relative to the secondportion and the second portion having a lower κ value than the firstportion. Both portions are formed having resistance to copper diffusion.

Other aspects and advantages of the invention will become apparent fromthe following detailed description and accompanying drawings whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description will be more readily understood inconjunction with the accompanying drawings, in which:

FIGS. 1( a) and 1(b) are simplified schematic cross-section views of aconventional copper interconnect structure illustrating the problem ofelectromigration induced void failures in conventional circuitstructures.

FIG. 2 is a simplified cross-sectional view of semiconductorinterconnect structure implementing a generalized embodiment of animproved dielectric barrier stack in accordance with the principles ofthe invention.

FIGS. 3( a)-3(e) are simplified cross-sectional views of semiconductorsubstrate illustrating a structure embodiment and process embodiment inaccordance with the principles of the invention.

FIGS. 4( a)-4(c) are simplified cross-sectional views of semiconductorsubstrate illustrating another structure and process embodiment inaccordance with the principles of the invention.

FIGS. 5( a)-5(d) are simplified cross-sectional views of semiconductorsubstrate illustrating more structure and process embodiments inaccordance with the principles of the invention.

FIG. 6 is a simplified figurative depiction of a semiconductor waferformed having interconnect structures and improved dielectric barrierlayers of the type described herein comprising part of its circuitry inaccordance with the principles of the invention.

It is to be understood that in the drawings like reference numeralsdesignate like structural elements. Also, it is understood that thedepictions in the Figures are not necessarily to scale.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention has been particularly shown and described withrespect to certain embodiments and specific features thereof. Theembodiments set forth hereinbelow are to be taken as illustrative ratherthan limiting. It should be readily apparent to those of ordinary skillin the art that various changes and modifications in form and detail maybe made without departing from the spirit and scope of the invention.

In the following detailed description, various method embodiments forforming conducting structures in semiconductor devices will bedisclosed. In particular, the depicted structures show the formation ofcopper conducting structures and improved dielectric barrier layers thatare suitable for use in a number of different modes. Particularly, suchimproved dielectric barrier layers find utility when used with theinterconnecting copper lines of multi-layer semiconductor devices. Theinventors specifically contemplate that the principles of the inventionare not strictly confined to copper materials but that they can also beapplied to copper-containing materials as well (e.g., copper alloys andlaminated copper structures that include more than just pure copper).The inventors also contemplate that the principles of the invention arenot limited to just interconnect and via structures, but that they canalso be applied to any interconnections between copper-containingconducting structures in a semiconductor substrate.

Referring again to FIG. 1( b), it has been determined that one of thekeys to suppressing the occurrence of void induced circuit failure incopper interconnect structures is the formation of barrier layers havingimproved adhesion to copper materials. One common site for copperelectromigration leading to void failure is at the interface between acopper layer of line and the barrier layers (“barrier layer” is usedhere collectively to refer to both dielectric barrier layer and metalbarrier layer). This is dramatically depicted in FIG. 1( b) whichschematically illustrates voids (depicted by the cross-hashed macrovoid108′) forming at the interface between the copper layer 107 and thebarrier layers (here metal barrier layer 110 and dielectric barrierlayer 111). As generalized proposition, the embodiments of the inventioninclude dielectric barrier layers having improved adhesion to coppermaterials. Such layers improve the electromigration lifetimes of coppercircuit structures.

FIG. 2 depicts one generalized embodiment, of a circuit structureincorporating an improved dielectric barrier layer. The structureincludes a dielectric stack formed on a copper layer. A substrate 200 isprovided and is typically constructed of a silicon wafer having one ormore layers of structure formed thereon. FIG. 2 depicts only theuppermost portions of what can be a multi-layered structure. In thedepicted embodiment, a copper layer 201 is formed on the substrate. Inthis depiction, the copper layer 201 is formed in an inlaid recess in aninsulating layer 202 formed on the substrate surface. Such structuresare commonly used in semiconductor fabrication. For example, suchstructure are commonly formed using damascene or dual-damascenefabrication processes. As depicted here, the copper layer 201 isdeposited into a recess formed in an insulating layer 202 comprised ofan electrically insulating material. Such insulating layers are commonlyreferred to as interlayer dielectric layers or ILD's. These insulatinglayers or ILD's 202 are formed of low-κ dielectric materials or otherelectrically isolating materials. The principles of the presentinvention find particular utility when applied to use with low-κdielectric materials. Examples of such materials include spin-on and CVDpolymeric materials based on silicon or carbon, or based on combinationsof silicon and carbon. Particular low-κ materials include, but are notlimited to: organic thermoplastic and thermosetting polymers such aspolyimides, polyarylethers, benzocyclobutenes, polyphenylquinoxalines,polyquinolines; inorganic and spin-on glass materials such assilsesquioxanes, silicates, and siloxanes; and, mixtures, or blends, oforganic polymers and spin-on glasses. Further, examples of CVD low-κmaterials include SiCOH or polymers of parylene and napthalene,copolymers of parylene with polysiloxanes or teflon, and polymers ofpolysiloxane. Other ILD 202 materials include, but are not limited to,silicon dioxide or combinations of silicon dioxide and other dopeddielectrics (e.g., BPSG, PSG).

In order to prevent the copper materials of the copper layer 201 fromcontaminating the ILD 202 barrier layers are used. Frequently, metalbarrier layers formed of titanium (e.g., Ti, TiN, and other relatedmaterials) or tantalum (e.g., Ta, TaN, TaSiN, and other relatedmaterials) based materials are used. Also, many other materials, such asCoWP (and others) are used to provide metal barrier layers for ILD's.Additionally, dielectric barrier layers can be used. In the depictedexample, metal barrier layers 203 are used and shown on the bottom andsidewalls of the recess. The use of such metal barrier layers is notcritical to the practice of the present invention but they are includedfor completeness.

Aspects of the present invention are directed to so-called dielectricbarrier layers which are also used to prevent copper from diffusing outof its intended location. As explained previously, dielectric barrierlayers differ from metal barrier layers in that dielectric barrierlayers do not incorporate refractory metals (W, Ti, Ta, Co, Mg, Pd, Cr,Mo, V, etc.) in their composition. Such dielectric barrier layersgenerally have a lower dielectric constant than do metal barrier layers.Such dielectric barrier layers are formed of materials that include, butare not limited to, amorphous hydrogenated silicon carbides; amorphoushydrogenated silicon oxycarbides; amorphous hydrogenated siliconnitrides; amorphous hydrogenated silicon carbon nitrides; certainorganic polymers (e.g., BCB) as well as other dielectric barriermaterials that provide a good electrical insulation between copper linesand operate as good diffusion barriers to copper. The use of suchdielectric barrier materials is advantageous in many processapplications

In the depicted embodiment, a dielectric barrier stack 205 of thepresent invention is shown. Typically, the dielectric barrier stack 205includes a first portion 206 (that lies adjacent to the copper layer201) and a second portion 207 formed on the first portion 206.Typically, but not exclusively, the first portion 206 includes a firstbarrier layer 206 that is formed along the top surface of the copperlayer 201. This first dielectric barrier layer 206 is formed of adielectric material that has good adhesion to the underlying copperlayer 201 and operates as a good diffusion barrier to copper.Additionally, it is helpful if the first dielectric barrier layer 206 isformed of a dielectric material having good adhesion to a subsequentlyformed second dielectric layer 207. Materials suitable for forming sucha first dielectric barrier layer 206 include, without limitation,amorphous hydrogenated silicon carbides, amorphous hydrogenated siliconcarbon nitrides, and amorphous hydrogenated silicon nitrides. Such firstdielectric barrier layers 206 are preferably formed very thin, on theorder of about 50 Å to about 100 Å. Although such a thin firstdielectric barrier layer 206 is preferred, the invention can bepracticed using thicker first dielectric barrier layers 206. Such layerscan be formed using a number of different method known to persons havingordinary skill in the art. In one example, the first dielectric barrierlayer 206 is formed using a PECVD technique.

The second portion 207 can comprise a second dielectric barrier layer207 formed of a different (second) dielectric barrier material. Thesecond dielectric barrier typically is chosen for its lower κ valuerelative to the first dielectric barrier layer 206. For example, seconddielectric barrier layers 207 can have κ values of less than about 4.Commonly, the second dielectric barrier 207 is formed to a greaterthickness than the underlying first dielectric barrier layer 206. Intypical embodiments, the second dielectric barrier 207 is formed in therange of 200-1000 {acute over (Å)}, preferably about 400 {acute over(Å)} thick. Thus, although the stack 205 has a somewhat high κ materialdirectly adjacent to the copper layer, in general, the overall stack 205is characterized by lower effective κ (due to the low κ value of thesubstantially thicker second dielectric barrier 207).

Examples of dielectric barrier materials suitable for use in a seconddielectric barrier layer 207 include, without limitation, porousamorphous hydrogenated silicon carbides and porous amorphoushydrogenated silicon nitrides. Additionally, any dielectric materialhaving a lower κ value than the first dielectric barrier layer 206 andproviding a good diffusion barrier to copper is suitable. Moreover, manyother low-κ materials serve as satisfactory materials for thefabrication of second dielectric barrier layers 207. Such materialsinclude spin-on and CVD polymeric materials based on silicon or carbon,or based on combinations of silicon and carbon. Particular low-κmaterials include, but are not limited to: organic thermoplastic andthermosetting polymers such as polyimides, polyarylethers,benzocyclobutenes (BCB), polyphenylquinoxalines, polyquinolines;inorganic and spin-on glass materials such as silsesquioxanes,silicates, and siloxanes; and, mixtures, or blends, of organic polymersand spin-on glasses. Further examples of CVD low-κ materials includeSiCOH or polymers of parylene and napthalene, copolymers of parylenewith polysiloxanes or teflon, and polymers of polysiloxane. Other usefulsecond dielectric barrier layer 207 materials include, but are notlimited to, silicon dioxide or combinations of silicon dioxide and otherdoped dielectrics (e.g., BPSG, PSG). Examples of such materials include,FLARE® and SiLK®.

Other embodiments can be used to form the depicted dielectric barrierstack 205. In particular, in such embodiments a first dielectric barrierlayer 206 can be formed and then plasma treated to enhance the adhesionof the first dielectric barrier layer 206 to the underlying copper layer201. As with the embodiment discussed above, the dielectric barrierstack 205 includes a first portion 206 (that lies adjacent to the copperlayer 201) and a second portion 207 formed on the first portion 206. Afirst barrier layer 206 is formed along the top surface of the copperlayer 201. Again the first dielectric barrier layer 206 is preferablyformed very thin, on the order of about 50 Å to about 100 Å. Althoughsuch a thin first dielectric barrier layer 206 is preferred, theinvention can be practiced using thicker first dielectric barrier layers206. This first dielectric barrier layer 206 is treated (e.g., plasmatreated) to improve its adhesion to the copper layer 201. Good adhesionrefers to high interfacial adhesion energy between two adjacent layers.In accordance with the principles of the invention, the first dielectricbarrier layer 206 has greater adhesion to copper than the seconddielectric barrier layer 207. Suitable materials and processes used forforming a suitable first dielectric barrier layer 206 will be discussedin detail hereinbelow.

As above, the dielectric barrier stack 205 includes a second portionformed on the first portion. In this implementation the second portioncomprises a second dielectric barrier layer 207 formed on the plasmatreated first dielectric barrier layer 206. The second dielectricbarrier layer 207 can be formed using ordinary dielectric barriermaterials and formed to a much greater thickness than the firstdielectric barrier layer 206. Typically, the second dielectric barrierlayer 207 is formed using the same dielectric barrier materials as areused to form the first dielectric barrier layer 206 with the exceptionthat the second dielectric barrier layer 207 is not treated to enhanceits adhesion properties. Alternatively, the second dielectric barrierlayer 207 is formed using different materials than are used to form thefirst dielectric barrier layer 206.

Again referring to FIGS. 1( a) and 1(b), during ordinary course ofoperation, the copper layer 107 in the via demonstrates a high densityof copper (Cu) ion flux. The presence of the barrier layers 110 and 111contributes significantly to the formation of voids at the metal/viainterconnect. It has been discovered that one significant contributoryfactor in electromigration problems in copper layers is the pooradhesion between the barrier layers 110, 111 and the associated copperconducting layers. An aspect of the present invention is directed toreducing the incidence of voiding and circuit failure in copperconducting structures and forming dielectric barrier layers that resultin improved electromigration lifetimes for copper conducting structuresin semiconductor devices.

The inventors have discovered that improved adhesion between adielectric barrier layer 111 and a copper-containing layer (e.g., 107)can result in a structure having a significantly improvedelectromigration lifetime. The inventors have discovered structures andfabrication methodologies related to improved dielectric barrier layers,examples of which are disclosed herein. In one such embodiment, animproved dielectric barrier stack having good adhesion to copper andgood dielectric performance is disclosed. In another related embodiment,an improved dielectric barrier stack having even greater adhesion tocopper at the cost of slightly reduced dielectric performance isdisclosed. Such embodiments can be fabricated by plasma treatingportions of the dielectric barrier stack with a plasma that includesdesired elements. In another related embodiment, an improved dielectricbarrier stack having improved adhesion to copper and improved dielectricperformance is fabricated by ion implanting selected ions.

FIGS. 3( a)-3(e) illustrate one method embodiment used for constructingan improved via/interconnect structure in accordance with the principlesof the invention. FIG. 3( a) depicts one example of a suitable substratein readiness for the formation of such an improved via/interconnectstructure. The substrate 300 typically comprises a copper line 311 overwhich barrier layers are formed. In the depicted embodiment, theconducting layer is a copper layer. One barrier layer 312 is adielectric barrier layer that is formed over the conducting layer 301.In other embodiments the barrier layer 312 can be formed of dielectricbarrier materials. An insulating layer 315 is formed on the substratesurface having an opening 314 formed therein. Such an opening 314permits the electrical connection with upper conducting layers withlower conducting layers. The insulating layer 315 is commonly formed ofelectrically insulating materials and is also referred to as aninter-layer dielectric (ILD). In many embodiments the ILD 315 is formedof low-K dielectric materials or other electrically isolating materials.The principles of the present invention find particular utility whenapplied to use with low-K dielectric materials. Examples of suchmaterials include spin-on and CVD polymeric materials based on siliconor carbon, or based on combinations of silicon and carbon. Particularlow-K materials include, but are not limited to: organic thermoplasticand thermosetting polymers such as polyimides, polyarylethers,benzocyclobutenes, polyphenylquinoxalines, polyquinolines; inorganic andspin-on glass materials such as silsesquioxanes, silicates, andsiloxanes; and, mixtures, or blends, of organic polymers and spin-onglasses. Further, examples of CVD low-K materials include SiCOH orpolymers of parylene and napthalene, copolymers of parylene withpolysiloxanes or teflon, and polymers of polysiloxane. Other materialsinclude, but are not limited to, silicon dioxide or combinations ofsilicon dioxide and other doped dielectrics (e.g., BPSG, PSG).

Openings 314 are formed in the ILD 315 to expose the underlyingconducting layers. Such openings 314 are typically formed usingmethodologies well known to those having ordinary skill in the art.Suitable techniques include, but are not limited to, damascene and dualdamascene fabrication processes. The openings expose a portion of theunderlying copper layer 311. Another copper diffusion barrier 313 isformed in the opening 314 to prevent copper material from diffusing intothe ILD 315. In some implementations, the copper diffusion barrier 313is formed of a metal barrier material to form a metal barrier layer.

A copper conducting layer (or plug) 301 is then formed in the opening314 to create an interconnect structure to the underlying copper line311. The copper layer 301 can be comprise of a wide range ofcopper-containing materials. One typical example is a copper layer 301that is comprised substantially of copper. However, the inventors pointout that such copper layers 301 can include, without limitation, copperalloy materials, multi-layer structures containing copper, as well asother like materials. Thus, the substrate 300 depicted in FIG. 3( a)provides one suitable embodiment of a starting substrate. Additionally,many other substrates having copper layers can enjoy the benefits of theinvention.

Reference is now made to FIG. 3( b). In many applications, the substrateis now pre-cleaned to remove native oxides. In particular, suchpre-cleaning is employed to remove a thin layer of copper oxide from theexposed portion of the copper layer 301. A typical approach forpre-cleaning involves plasma treating the surface with a plasma 320 ofreducing gases (e.g., NH₃ and H₂). Additionally, the surface can betreated with a plasma 320 formed using argon, hydrogen, or carbonfluoride (CF_(x)) materials. Such plasma cleaning should be conducteduntil about 50 Å of oxide are removed from the copper layer 301.Techniques for achieving such pre-cleaning are known to persons havingordinary skill in the art. This substrate can have a dielectric barrierstack in accordance with the principles of the invention formed thereon.

FIG. 3( c) illustrates one portion of the process of forming adielectric barrier stack in accordance with the principles of theinvention. A first dielectric barrier layer 206 is formed on the on thesubstrate. In particular, the first dielectric barrier layer 206 isformed having a relatively thin dimension with a layer thickness ofabout 50-100 Å thick. In alternative embodiments, a thicker firstdielectric barrier layer 206 can be employed.

One suitable process for applying the first dielectric barrier layer 206is plasma enhanced chemical vapor deposition. Other techniques, such asstandard chemical vapor deposition processes can be used. Suitablemachines for accomplishing such layer formation include chemical vapordeposition (CVD) or plasma enhanced chemical vapor deposition (PECVD)machines. Examples of satisfactory machines are Sequels (manufactured byNovellus Systems, Inc. of San Jose, Calif.); Centura 5000 or Producer(manufactured by Applied Materials, Inc. of Santa Clara, Calif.); orTrikon FXP (manufactured by Trikon Technologies, Inc. of the UnitedKingdom).

In accordance with one embodiment of the present invention, a siliconcarbide material or a silicon oxycarbide material can be used to form apreferred first dielectric barrier layer 206. Silicon carbide, forpurposes of this patent, is a generic name given to a class of materialscomprising amorphous hydrogenated silicon carbides. Also, for purposesof this patent, silicon oxycarbide is a generic name given to a class ofmaterials comprising amorphous hydrogenated silicon oxycarbides. Thefollowing discussion is directed toward one example of a method offorming such layers. In a plasma enhanced chemical vapor deposition(PECVD) process a substrate 300 is positioned in a processing chamber ofa PECVD machine and appropriate reactant materials are flowed into thechamber. The reactant materials are ignited into plasma and a dielectricbarrier material is deposited to form layer 206.

Suitable precursor materials include silicon-containing materials andmethylated materials. For example, methane and silane can be flowed andignited together to achieve desired films. Another class of precursormaterials are methyl silanes. For example, 4-methylsilane (Si(CH)₄, alsoknown as 4MS), 3-methylsilane (Si(CH)₃H, also known as 3MS),2-methylsilane (Si(CH)₂H, also known as 2MS), and also 1-methylsilane(Si(CH)H₃, also known as 1MS). In one exemplar process, precursormaterials are flowed into the process chamber with an inert carrier gas(e.g., argon (Ar) or helium (He)). Additionally, if a silicon oxycarbidelayer is desired, another reactant, oxygen (O₂) gas is flowed into thechamber. For example, Si(CH)₃H (3MS) is flowed into the chamber with anAr carrier gas while O₂ gas is flowed into the chamber.

In one suitable process embodiment, a silicon carbide dielectric barrierlayer 206 is formed by flowing 3MS into the chamber at a rate of about400 SCCM (standard cubic centimeter per minute) with an Ar carrier gasflow rate of about 1500 SCCM. The forgoing embodiment is but onepreferred implementation. 3MS flow rates can range from about 10 SCCM toabout 1000 SCCM. Carrier gas flow rates can range from about 50 SCCM toabout 3000 SCCM. Additionally, O₂ gas flow rates can range from about 10SCCM to about 1000 SCCM, in order to achieve suitable silicon oxycarbidedielectric barrier layers. As the materials are flowed into the processchamber, a pressure in the range of about 0.1-10 Torr, preferably about6 Torr is maintained. A plasma is then ignited in the chamber. Asuitable plasma ignition power ranges from about 200 watts (W) to about600 W, with a preferred power being about 300 W. After plasma ignition,a silicon carbide can be deposited to a desired thickness, withpreferred thicknesses being in the range of about 50 Å to about 100 Å.But as indicated hereinabove, thicknesses of greater than 100 Å can alsobe used. One typical process takes about 5 seconds to deposit a siliconcarbide first dielectric barrier layer 206 to about 100 Å. It should benoted that many other techniques can be used to fabricate suitabledielectric barrier layers (e.g., See, U.S. Pat. No. 5,926,740 to Forbes,et al. which describes methods of SiOC and SiC formation).

Alternatively, silicon nitrides (Si_(x)N_(y)) and silicon carbonnitrides (Si_(x)C_(y)N_(z)) or other like materials can be used to formsuitable first dielectric barrier layers 206. Such dielectric barrierlayers 206 can be formed using conventional approaches. For example asilicon nitride dielectric barrier layer 206 can be formed using PECVD,CVD, physical vapor deposition (PVD) or atomic layer deposition (ALD)techniques

The thin first dielectric barrier layer 206 is then plasma treated withappropriate adhesion enhancing materials to increase the adhesion of thedielectric barrier layer 206 to the underlying copper layer 301. Thiscan be accomplished using the same process tools used to form thedielectric barrier layer 206. Examples of such adhesion enhancingmaterials include, but are not limited to, carbon, nitrogen, hydrogen,phosphorus, sulfur as well as other materials that result in increasedadhesion to copper. Of particular utility are carbon and nitrogencontaining materials. Typically, such adhesion enhancement can be had byplasma treating the first dielectric barrier layer 206 with a plasmahaving a high concentration of adhesion enhancing ions. Such plasmatreatment increases the concentration of such materials in a firstdielectric barrier layer 206. As a result, the adhesion of the firstdielectric barrier layer 206 to copper can be increased. This has theeffect of reducing the effect of copper electromigration and voidinduced circuit failure.

With reference to FIG. 3( d) an example plasma treatment process isdisclosed. In one suitable process embodiment, a first dielectricbarrier layer 206 plasma treated by flowing a suitable adhesionenhancing materials (e.g., a carbon or nitrogen containing material)into the chamber and then igniting the material to form a plasma 350.The plasma 350 interacts with the first dielectric barrier layer 206 toincrease the concentration of the desired materials in the firstdielectric barrier layer 206. Plasmas demonstrating a relatively highmean free path (MFP) are desired. Such plasmas can be achieved usingrelatively low pressure processes.

If the process engineer decides to increase the nitrogen content of thefirst dielectric barrier layer 206, nitrogen-containing materials suchas N₂, NH₃, or other nitrogen-containing materials can be used. A lesspreferred, but still useful implementation uses nitrogen-containingmaterials having oxygen (e.g., N₂O). In an alternative approachcarbon-containing materials can be used. Typical examples, include, butare not limited to, hydrocarbons. A preferred implementation usesmaterials such as CH₄, C₂H₆, C₃H₈, and so on. A less preferred, butstill useful implementation uses carbon-containing materials havingoxygen (e.g., CO, CO₂). Additionally, both the carbon and nitrogencontent of the first dielectric barrier layer 206 can be increased.Additionally, in some implementations it is advantageous to flow sulfurand/or phosphorus containing compounds into the chamber to increase thesulfur or phosphorus content of the first dielectric barrier layer 206.Such films also demonstrate increased adhesion to copper.

In one example process, an N₂ gas is flowed into the chamber at a flowrate of in the range of about 2 SCCM to about 5000 SCCM. In one example,N₂ gas is flowed into the chamber at rate of about 400 SCCM. Thepressure should be maintained at a range of about 1 mTorr to 10 Torr. Aplasma is then ignited in the chamber. A suitable plasma ignition powerranges from about 50 watts (W) to about 3000 W, with a preferred powerbeing about 100 W with pressure of about 100 mTorr. After plasmaignition, the first dielectric barrier layer 206 is exposed to thenitrogen plasma. Optionally, the plasma can be subject to a low biasvoltage (e.g., less than about 100 V). Such exposure increases thenitrogen content of the first dielectric barrier layer 206. Similarprocess parameters can be used to increase the carbon, phosphorus, orsulfur content of the first dielectric barrier layer 206. A typicalplasma treatment takes about 1 s (second) to about 60 s. A 5 secondexposure is generally sufficient to achieve an effective concentrationof adhesion enhancing materials. In particular, adhesion enhancingmaterials such as carbon and nitrogen are preferred because the increasethe adhesion of first dielectric barrier layer 206 without substantiallyincreasing the K value of the first dielectric barrier layer 206.Consequently, the adhesion is increased without a substantial sacrificeof dielectric performance in the first dielectric barrier layer 206.

As depicted in FIG. 3( e), after plasma treatment, a bulk seconddielectric barrier layer 207 is formed on the first dielectric barrierlayer 206. Typically, this second dielectric barrier layer 207 is formedhaving a much greater thickness than the thin first dielectric barrierlayer 206. Typical thickness dimensions for the second dielectricbarrier layer 207 are in the range of about 200 Å to about 500 Å. Thesecond dielectric barrier layer 207 is typically formed out of the samematerial as the first dielectric barrier layer 206 prior to plasmatreatment. However, the inventors contemplate that other dielectricbarrier materials can be used to form the second dielectric barrierlayer 207. In either case, the process parameters described herein abovewith respect to forming the first dielectric barrier layer 206 (See,FIG. 3( c) and the discussion pertaining thereto) can be implemented toform suitable second dielectric barrier layers 207.

FIGS. 4( a)-4(c) illustrate another method embodiment used forconstructing an improved via/interconnect structure in accordance withthe principles of the invention. FIG. 4( a) depicts a suitable substratesuch as described earlier with respect to FIGS. 3( a) and 3(b). Thissubstrate then has a first dielectric barrier layer 406 formed thereon.Such first dielectric barrier layers 406 are preferably formed usingPECVD or atomic layer deposition (ALD) techniques. Such layers arepreferably formed having a adhesion to underlying copper layers 301.SiCN and SiC layers are therefore preferred. However, other dielectricbarrier materials can be used to form the first dielectric barrier layer406. As will previous first dielectric barrier layers, such layers arepreferrably formed having relatively thin having a layer thickness ofabout 50-100 Å thick. However, alternative embodiments having thickerfirst dielectric barrier layers 406 can be employed.

With reference to FIG. 4( b), an example plasma treatment process isdisclosed. As with the previously described process embodiments, thefirst dielectric barrier layer 406 plasma treated by flowing a suitableadhesion enhancing materials (e.g., a carbon or nitrogen containingmaterial) into the chamber and then igniting the material to form aplasma 450. The plasma 450 interacts with the first dielectric barrierlayer 406 to increase the concentration of the desired materials in thefirst dielectric barrier layer 406. Such processes as previouslydescribed can be used. In such embodiments, where improved adhesion isdesired at the cost of slightly reduced dielectric performance (i.e.,the K is increased) adhesion enhancing materials having lower hydrogencontent can be used. Particularly attractive in such implementations arenitrogen-containing materials such as N₂ gas. In less preferredalternatives, nitrogen-containing materials having oxygen (e.g., N₂O)can be used. Additionally, carbon-containing materials having oxygen(e.g., CO, CO₂) are useful. Additionally, sulfur and/or phosphoruscontaining compounds can be flowed into the chamber to increase thesulfur or phosphorus content of the first dielectric barrier layer 406.Such films demonstrate increased adhesion to copper at the cost ofmoderately decreased dielectric performance. Generally, such reduceddielectric performance is offset by the fact that the first dielectricbarrier layer 406 is very thin. Thus, a great deal of the dielectricperformance of the resulting dielectric barrier stack is provided by thelow K second dielectric barrier layer. Such dielectric barrier stackshave still longer electromigration lifetimes.

Once the first dielectric barrier layer 406 is formed and plasmatreated, a second dielectric barrier layer 407 is formed to complete thedielectric stack 408. Such a structure is depicted in FIG. 4( c). Suchsecond dielectric barrier layers 407 can be formed as described in thediscussions of FIG. 3( e). As previously discussed such seconddielectric barrier layers 407 can be bulk deposited having a greaterthickness than the first dielectric barrier layer 406. Thus, theslightly reduced dielectric performance (i.e., higher K) of the firstdielectric barrier layer 406 is offset by the fact that dielectric stack408 also includes a second dielectric barrier layer 407 having superiordielectric performance (i.e., lower K) and greater thickness. Thus, thefirst dielectric barrier layer 406 provides superior adhesion to thecopper layer 301 while the second dielectric barrier layer 407 provideslow K. Thus the resulting dielectric barrier stack 408 reaps thebenefits of both superior adhesion to copper and low K.

In yet another embodiment, the structure depicted in either FIG. 3( c)or FIG. 4( a) can be used as the starting point. Such structures beingformed by any of the previously disclosed methods or other suitablemethods. The embodiment depicted in FIG. 5( a) includes a substrate 500having been formed, for example, as in the processes leading up toeither FIG. 3( c) or FIG. 4( a). The substrate 500 is shown with acopper layer 301 having a first dielectric barrier layer 506 formedthereon. As explained such layers 506 can be formed using methodsalready described.

Referring to FIG. 5( b) the concentration of adhesion enhancingmaterials (such as previously described) in the first dielectric barrierlayer 506 is enhanced by means of ion implantation. Adhesion enhancingions 501 (e.g., carbon, nitrogen, hydrogen, phosphorus, sulfur, andother materials that enhance the adhesion of dielectric barrier layersto copper) are implanted into the first dielectric barrier layer 506 toincrease the concentration of such materials in the first dielectricbarrier layer 506. Since the first dielectric barrier layer 506 isrelatively thin, low implantation energies are all that is required toincrease the concentration of such materials in the first dielectricbarrier layer 506. For example, in a first dielectric barrier layer 506having a thickness of about 100 Å an ion implantation energy fornitrogen ions is in the range of about 1000 eV (electron volts) to about100,000 eV. Effective dosages are in the range of about 1×10¹⁶ to about2×10²⁰ ions per cm².

Additionally, as depicted in FIG. 5( b), by selectively adjusting theimplantation voltages used for implantation of the adhesion enhancingmaterials, the implanted adhesion materials can be preferentiallylocated in a desired implantation region 502 (indicated by the X's)right at the interface between the first dielectric barrier layer 506and the copper layer 301. Thus, the adhesion enhancing materials can beconcentrated right at the location where they will have the most effectadhesion enhancing effect. Additionally, by making the desiredimplantation region 502 very narrow, the effect on the dielectricproperties of the first dielectric barrier layer 506 is also reduced.The precise energies required to accomplish such implantation depend ona number of factors known to persons having ordinary skill in the artand include, but are not limited to thickness of the first dielectricbarrier layer 506, type of ion implanted, depth and width of the desiredimplantation region 502 as well as other factors.

FIG. 5( c) schematically depicts the next step in the formation of thedielectric barrier stack 508. In FIG. 5( c), a second dielectric barrierlayer 507 is formed on the first dielectric barrier layer 506 tocomplete the dielectric barrier stack 508. As described previously, suchsecond dielectric barrier layers 507 can be formed using any of themethods previously described.

FIG. 5( d) depicts yet another embodiment related to that of FIGS. 5(a)-5(c). The depicted embodiment uses but a single dielectric barrierlayer 510 formed at a final desired thickness. Generally, in the rangeof about 50 Å to about 1000 Å, preferably about 500 Å. The singledielectric barrier layer 510 is then implanted with adhesion enhancingions 511 (e.g., carbon, nitrogen, hydrogen, phosphorus, sulfur, andother materials that enhance the adhesion of dielectric barrier layersto copper) increase the concentration of such materials. Suchimplantation can be accomplished as described hereinabove. Again, byselectively adjusting the implantation voltages used for implantation ofthe adhesion enhancing materials, the implanted adhesion materials canbe preferentially located in a desired implantation region 512(indicated by the X's) right at the interface between the singledielectric barrier layer 510 and the copper layer 301. Due to thegreater thickness of the single dielectric barrier layer 510, theprecise energies required to accomplish such implantation arecorrespondingly increased. Such a structure has the advantage of havinghigh adhesion (adhesion energy) with copper and excellent dielectricproperties. Such a structure provides increased electromigrationlifetimes for circuit devices. The single dielectric barrier layer canbe formed using dielectric barrier layer fabrication processes known topersons having ordinary skill in the art including, but not limited tofabrication methods discussed elsewhere in this patent.

Referring to FIG. 6, a semiconductor wafer is depicted. Typically, suchwafers 601 having a multiplicity of integrated circuits (chips) 602formed thereon. Each chip has many different types of circuit structuresformed thereon. Accordingly, each chip 502 can include structures suchas schematically depicted in FIGS. 2, 3(e), 4(c), 5(c) and 5(d) (shownschematically depicted here as interconnect structures 603) as part ofits structure.

Thus, embodiments of the invention include dielectric barrier layershaving increased amounts of adhesion enhancing materials formed in theirstructure. As a result, such structures improve the electromigrationlifetimes of copper conducting structures incorporating such improveddielectric barrier layers.

The present invention has been particularly shown and described withrespect to certain preferred embodiments and specific features thereof.However, it should be noted that the above-described embodiments areintended to describe the principles of the invention, not limit itsscope. Therefore, as is readily apparent to those of ordinary skill inthe art, various changes and modifications in form and detail may bemade without departing from the spirit and scope of the invention as setforth in the appended claims. Other embodiments and variations to thedepicted embodiments will be apparent to those skilled in the art andmay be made without departing from the spirit and scope of the inventionas defined in the following claims. In particular, it is contemplated bythe inventors that dielectric barrier layers in accordance with theprinciples of the present invention can be practiced with a number ofdifferent materials and formed by a wide variety of methods. Moreover,the adhesion enhancing materials used in conjunction with suchdielectric barrier layers can be selected from among carbon, nitrogen,hydrogen, phosphorous, and sulfur containing materials, as well as othermaterials that enhance the adhesion of dielectric barrier layers tocopper. Further, reference in the claims to an element in the singularis not intended to mean “one and only one” unless explicitly stated, butrather, “one or more”. Furthermore, the embodiments illustrativelydisclosed herein can be practiced without any element which is notspecifically disclosed herein.

1. A copper interconnect structure having increased electromigrationlifetime, the interconnect comprising: a semiconductor substrate; acopper layer formed on the substrate; and a dielectric barrier stackformed on top of the copper layer, said dielectric barrier stackincluding a first portion consisting of a single first barrier layerformed adjacent to the copper layer and a second portion consisting of asingle second barrier layer formed on the single first barrier layer,the first portion having improved adhesion to copper relative to thesecond portion, the second portion having a lower κ value relative tothe κ value of the first portion and both portions being formed havingresistance to copper diffusion and wherein the first portion hasincreased concentration of at least one of phosphorus and sulfurrelative to the second portion of the barrier stack.
 2. A copperinterconnect structure having increased electromigration lifetime, theinterconnect comprising: a semiconductor substrate; a copper layerformed on the substrate; and a dielectric barrier stack formed on top ofthe copper layer, said dielectric barrier stack including a firstportion formed adjacent to the copper layer and a second portion formedon the first portion, the first portion having improved adhesion tocopper relative to the second portion, the second portion having a lowerκ value relative to the κ value of the first portion and both portionsbeing formed having resistance to copper diffusion; wherein the bothportions of the barrier stack are each comprised of a material selectedfrom among silicon carbide, silicon carbon nitride, silicon dioxide, andsilicon nitride; and wherein the first portion is formed havingincreased adhesion to the copper layer achieved by having a greaterconcentration of at least one of phosphorus and sulfur relative to thesecond portion of the barrier stack.
 3. The structure of claim 1 whereinthe first portion has been ion implanted to increase its concentrationof at least one of phosphorus and sulfur relative to the second portionof the barrier stack thereby increasing its adhesion to copper andincreasing its dielectric constant relative to the second portion of thestack and wherein the second portion comprises a thicker dielectricbarrier layer comprised of a dielectric barrier material that has notbeen ion implanted in the same way as the first portion.
 4. Asemiconductor integrated circuit incorporating the structure of claim 3.5. A copper interconnect structure having increased electromigrationlifetime, the interconnect comprising: a semiconductor substrate; acopper damascene structure formed in recesses formed in the substrate; afirst barrier layer having first portion formed on top of thesemiconductor substrate and in contact with the copper damascenestructure and having good adhesion to the copper of the copper damascenestructure and having resistance to copper electromigration and alsohaving a first κ value; and the barrier layer including a second portionarranged in contact with and above the first portion and having a secondκ value and having resistance to copper electromigration, the firstportion including a concentration of dopant materials wherein saiddopant materials include at least one of phosphorus and sulfur.
 6. Acopper interconnect structure having increased electromigrationlifetime, the interconnect comprising: a semiconductor substrate; acopper damascene structure formed in recesses formed in the substrate; afirst barrier layer formed on top of the semiconductor substrate and incontact with the copper damascene structure, the first barrier layerhaving good adhesion to the copper of the copper damascene structure andhaving resistance to copper electromigration and also having a first κvalue; a second barrier layer formed on top of the semiconductorsubstrate and in contact with the first barrier layer and having asecond κ value and having resistance to copper electromigration; saidfirst and second layers comprising a dielectric barrier stack with thefirst barrier layer having improved adhesion to copper relative to thesecond barrier layer, and wherein the second κ value of the secondbarrier layer has a lower value than the first κ value of the firstbarrier layer and having improved resistance; wherein the first andsecond layers of the barrier stack are each comprised of a materialselected from among silicon carbide, silicon carbon nitride, silicondioxide, and silicon nitride; and wherein the first barrier layer has agreater concentration of at least one of phosphorus and sulfur relativeto the second barrier layer thereby increasing the adhesion of the firstbarrier layer to copper relative to the second barrier layer.
 7. Thestructure of claim 6 wherein the first barrier layer is formed of a verythin profile of in the range of about 50 Å to about 100 Å.
 8. Thestructure of claim 6 wherein the first barrier layer is formed of a verythin profile of about 50 Å.
 9. The structure of claim 6 wherein thesecond barrier layer is formed to a greater thickness than the firstbarrier layer.
 10. The structure of claim 6 wherein the second barrierlayer is formed to a thickness in the range of about 200 Å to about 1000Å.
 11. The structure of claim 6 wherein the first barrier layer has agreater concentration of phosphorus relative to the second barrierlayer.
 12. The structure of claim 6 wherein the first barrier layer hasa greater concentration of sulfur relative to the second barrier layer.13. A semiconductor integrated circuit incorporating the structure ofclaim
 3. 14. A semiconductor integrated circuit incorporating thestructure of claim 6.